The most common approach for air conditioning the interior of a bus is to mount the air conditioning components on the roof of the vehicle. It has been the common practice in the industry to locate the compressor for the unit in the vehicles motor compartment so that it can be driven directly from the engine. The compressor, in turn, must be connected to the air conditioning unit by means of refrigerant supply and return lines. This requires running an extensive amount of piping through the bus between the engine compartment and air conditioner.
In addition, the evaporator coil that is contained in the rooftop unit can also generate a good deal of condensate which must be disposed of in someway. In many prior art rooftop air conditioning systems, the condensate produced by the evaporator coil is collected in the floor panel or pan of the unit and is drained to the exterior of the vehicle by means of drainage hoses. The drainage often times runs over the surface of the vehicle producing unwanted stains and films windows which can be hazardous. Typically, the rooftop air conditioners are relatively large units having a high profile which produces a good deal of drag even as the vehicle moves at a relatively low speed.